Solid-State Imaging Spectrometer Research Articles

ROSAT and ASCA Observations of a Narrow-Line Seyfert 1 Galaxy RX J0136.9-3510: Blueshifted Fe Kα Line and Extended Soft X-Ray Emission

RX J0136.9-3510 is an unusual narrow-line Seyfert 1 galaxy (NLS1). We have detected extended (~12'' or ~54 kpc at the source frame) soft X-ray emission in the ROSAT High Resolution Imager image, accounting for 20% of the total emission. We have also detected a highly blueshifted (7.6 keV in the source frame) Fe K α line in the ASCA Solid-State Imaging Spectrometer spectrum. This is the first detection of such a highly blueshifted emission line in a NLS1. Near-IR and far-IR studies indicate the presence of a possible starburst component in this NLS1. Physical models of the accretion and/or outflow and of the evolution of this NLS1 are discussed in the context of these results.

Optical Identification of theASCALynx Deep Survey: An Association of Quasi‐Stellar Objects and a Supercluster at \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $z=1.3$ \end{document} ?

Results of optical identification of the ASCA Lynx Deep Survey are presented. Six X-ray sources are detected in the 2-7 keV band using the Solid-State Imaging Spectrometer in a ~20' × 20' field of view with fluxes larger than ~4 × 10-14 ergs s-1 cm-2 in the band. Follow-up optical spectroscopic observations were made, and five out of six sources are identified with active galactic nuclei/quasi-stellar objects (AGNs/QSOs) at redshifts of 0.5-1.3. We also identify two more additional X-ray sources detected in a soft X-ray band with AGNs/QSOs. We find that three QSOs identified are located at z ~ 1.3. Two rich clusters and several groups of galaxies are also placed at the same redshift in the surveyed field, and projected separations between the QSOs and the clusters are 3-8 Mpc at the redshift.

X‐Ray Spectrum of Supernova 1993J Observed withASCAand Its Evolution 8–572 Days after the Explosion

ASCA observations of the supernova in M81, SN 1993J, 8-572 days after the explosion are presented. Utilizing a one-dimensional image-fitting to the Solid-State Imaging Spectrometer (SIS) data, energy spectra of the supernova in 0.5-8 keV are obtained. The spectrum showed drastic softening with a power-law photon index of 0.3-4, while the X-ray intensity decreased from 0.03 to 0.008 counts s-1 SIS-1. The early phase of spectra requires two thermal emission components of different absorption columns if they are fitted with thermal models. The temperatures of two emission components cannot be well constrained with ASCA continuum spectra. However, the detection of an iron K emission line with ASCA and the hard X-ray spectra observed by OSSE on the Compton Gamma-Ray Observatory suggest that the two components have different temperatures: a few keV and about 100 keV. The properties of the two emission components are consistent with emissions from the front and reverse shocks of the supernova explosion. The drastic softening of the X-ray spectra is explained by the decrease of the absorption column density of the reverse shock component and the change of the major contributor to the soft X-ray band from the front to the reverse shocks.

The Sun as an X‐Ray Star. IV. The Contribution of Different Regions of the Corona to Its X‐Ray Spectrum

We study X-ray-synthesized spectra of solar regions as templates to interpret analogous stellar spectra. We define three classes of coronal structures of different brightness, low (background quiet corona), medium (active regions), and high (active region cores), and determine their contribution to the solar X-ray emission measure versus temperature, EM(T), luminosity, and spectrum. This study defines the extent of the solar analogy quantitatively and accurately. To this end, we have selected a large sample of full-disk Yohkoh soft X-ray telescope observations taken between the maximum and the minimum of solar cycle 22, obtaining the contribution of each class to the whole Sun's EM(T). From the EM(T) distributions, we synthesize the X-ray spectra of the Sun and of the single classes of solar coronal regions as they would be collected with the ROSAT Position Sensitive Proportional Counter (PSPC) and ASCA Solid-State Imaging Spectrometer. We find that the Sun during the cycle fits well in the stellar scenario as a low-activity star. The ROSAT PSPC hardness ratio (HR) and surface X-ray flux, FPSPC, both increase going from the background corona to the active regions and the cores of the active regions, and range between the values of low and intermediate activity stars. We suggest that the coronae of these stars may be explained as the effect of structures similar to those present on the Sun and that the various levels of X-ray luminosity, HR, and FPSPC are achieved by changing the surface coverage of the different classes of coronal regions.

ITAL]CHANDRA[/ITAL][ITAL]Chandra[/ITAL] and [ITAL]ASCA[/ITAL] X-Ray Observations of the Type II-L Supernova SN 1979C in NGC 4321

We report on the X-ray observation of the radio-selected supernova SN 1979C carried out with ASCA in 1997 December and serendipitously available from a Chandra Guaranteed Time Observation in 1999 November. The supernova, of type SN II-linear (SN II-L), was first observed in the optical and occurred in the weakly barred, almost face-on spiral galaxy NGC 4321 (M100). The galaxy, a member of the Virgo S Cluster, is at a distance of 17.1 Mpc and contains at least three other supernovae discovered in this century. The useful exposure time was ~25 ks for the Solid-State Imaging Spectrometer (SIS), ~28 ks for the Gas Scintillation Imaging Spectrometer, and ~2.5 ks for the Chandra Advanced CCD Imaging Spectrometer. No point source was detected at the radio position of SN 1979C in a 3' diameter, half-power response circle in the ASCA data. The background- and galaxy-subtracted supernova (SN) signal had a 3 σ upper limit to the flux of 6.3 × 10-14 ergs cm-2 s-1 in the full ASCA SIS band (0.4–10.0 keV) and a 3 σ upper limit of less than (3–4) × 10-14 erg cm-2 s-1 in the 2–10 keV band. In the Chandra data, a source at the position of SN 1979C is marginally detected at energies below 2 keV at a flux consistent with the ROSAT HRI detection in 1995. At energies above 2 keV, no source is detected with an upper limit of ~3 × 10-14 ergs cm-2 s-1. These measurements give the first ever X-ray flux limit of a Type II-L SN above 2 keV, which is an important diagnostic of the outgoing shock wave plowing through the circumstellar medium.

X‐Ray Energy Spectra of the Supersoft X‐Ray Sources CAL 87 and RX J0925.7−4758 Observed withASCA

We report observation results of the supersoft X-ray sources CAL 87 and RX J0925.7-4758 with the X-ray CCD cameras (Solid-State Imaging Spectrometers [SISs]) on board ASCA. Because of the superior energy resolution of the SIS (ΔE/E ~ 10% at 1 keV) relative to previous instruments, we could study detailed X-ray spectral structures of these sources for the first time. We have applied theoretical spectral models to CAL 87 and constrained the white dwarf mass and intrinsic luminosity as 0.8-1.2 M☉ and 4 × 1037-1.2 × 1038 ergs s-1, respectively. However, we have found the observed luminosity is an order of magnitude smaller than the theoretical estimate, which indicates that the white dwarf is permanently blocked by the accretion disk, and we are observing a scattering emission by a fully ionized accretion disk corona (ADC) whose column density is ~1.5 × 1023 cm-2. Through simulation we have shown that the orbital eclipse can be explained by the ADC model, such that a part of the extended X-ray emission from the ADC is blocked by the companion star filling its Roche lobe. We have found that very high surface gravity and temperature, ~1010 cm s-2 and ~100 eV, respectively, as well as a strong absorption edge at ~1.02 keV, are required to explain the X-ray energy spectrum of RX J0925.7-4758. These values are only possible for an extremely heavy white dwarf near the Chandrasekhar limit. Although the supersoft source luminosity should be ~1038 ergs s-1 at the Chandrasekhar limit, the observed luminosity of RX J0925.7-4758 is nearly 2 orders of magnitude smaller, even assuming an extreme distance of ~10 kpc. To explain the luminosity discrepancy, we propose a model in which very thick matter that was previously ejected from the system, as a form of jets, intervenes the line of sight and reduces the luminosity significantly because of Thomson scattering.

ITAL]Chandra[/ITAL] Observations of the Gravitationally Lensed System 2016+112

An observation of the gravitationally lensed system 2016+112 with the Chandra X-Ray Observatory has resolved a mystery regarding the proposed presence of a dark matter object in the lens plane of this system. The Chandra Advanced CCD Imaging Spectrometer observation has clearly detected the lensed images of 2016+112 with positions in good agreement with those reported in the optical and also detects 13 additional X-ray sources within a radius of 35. Previous X-ray observations in the direction of 2016+112 with the ROSAT HRI and ASCA Solid-State Imaging Spectrometer have interpreted the X-ray data as arising from extended emission from a dark cluster. However, the present Chandra observation can account for all the X-ray emission as originating from the lensed images and additional point X-ray sources in the field. Thus, cluster parameters based on previous X-ray observations are unreliable. We place a 3 σ upper limit on the 2-10 keV flux and luminosity of the cluster of 1.6 × 10-14 ergs s-1 cm-2 and 1.7 × 1044 ergs s-1, respectively. We estimate an upper limit on the mass-to-light ratio within a radius of 800 h kpc of M/LV < 190 h50 (M/LV)☉. None of the additional point X-ray sources are associated with the galaxy cluster members recently detected in deep optical and IR observations.

The Decrease in X-Ray Flux of the Accretion-powered Millisecond Pulsar SAX J1808.4−3658 in Quiescence Detected by [ITAL]ASCA[/ITAL

The accretion-powered millisecond X-ray pulsar SAX J1808.4-3658 was observed in quiescence with ASCA in 1999 September. We detected a dim X-ray source in the Solid-State Imaging Spectrometer (SIS) data at the position consistent with SAX J1808.4-3658. The source count rate was (1.1 ± 0.4) × 10-3 counts s-1 (0.5-5 keV) for a single SIS, which corresponds to (3 ± 1) × 10-14 ergs s-1 cm-2 if a power-law energy spectrum of photon index 2 with low-energy absorption corresponding to a hydrogen column density of 1.3 × 1021 cm-2 is assumed. The statistical quality of the data was insufficient to constrain the energy spectrum or to detect the 401 Hz coherent pulsation. We compare the data with the BeppoSAX observation also made during the quiescent state and find that the X-ray flux measured by ASCA is at least a factor of 4 smaller than that measured by BeppoSAX. We discuss the possible X-ray emission mechanisms that could explain the flux change, including the radio pulsar and the radio pulsar shock emission.

Restoration of theASCASource Position Accuracy

We present a calibration of the absolute pointing accuracy of the Advanced Satellite for Cosmology and Astrophysics (ASCA) which allows us to compensate for a large error (up to 1') in the derived source coordinates. We parameterize a temperature dependent deviation of the attitude solution which is responsible for this error. By analyzing ASCA coordinates of 100 bright active galactic nuclei, we show that it is possible to reduce the uncertainty in the sky position for any given observation by a factor of 4. The revised 90% error circle radius is then 12'', consistent with preflight specifications, effectively restoring the full ASCA pointing accuracy. Herein, we derive an algorithm which compensates for this attitude error and present an internet-based table to be used to correct post facto the coordinate of all ASCA observations. While the above error circle is strictly applicable to data taken with the on-board Solid-state Imaging Spectrometers (SISs), similar coordinate corrections are derived for data obtained with the Gas Imaging Spectrometers (GISs), which, however, have additional instrumental uncertainties. The 90% error circle radius for the central 20' diameter of the GIS is 24''. The large reduction in the error circle area for the two instruments offers the opportunity to greatly enhance the search for X-ray counterparts at other wavelengths. This has important implications for current and future ASCA source catalogs and surveys.

The X‐Ray Spectrum and Global Structure of the Stellar Wind in Vela X‐1

We present a quantitative analysis of the X-ray spectrum of the eclipsing high mass X-ray binary Vela X-1 (4U 0900-40) using archival data from the ASCA Solid-State Imaging Spectrometer. The observation covers a time interval centered on the eclipse of the X-ray pulsar by the companion. The spectrum exhibits two distinct sets of discrete features: (1) recombination lines and radiative recombination continua from mostly hydrogenic and helium-like species produced by photoionization in an extended stellar wind; and (2) fluorescent K-shell lines associated with near-neutral species also present in the circumsource medium. These features are superposed on a faint continuum, which is most likely nonthermal emission from the accreting neutron star that is scattered into our line of sight by free electrons in the wind. Using a detailed spectral model that explicitly accounts for the recombination cascade kinetics for each of the constituent charge states, we are able to obtain a statistically acceptable (χ = 0.88) fit to the observed spectrum and to derive emission measures associated with the individual K-shell ions of several elements. From calculations of the ionization balance using the photoionization code, XSTAR, we assign ionization parameters, ξ, to several ions, and construct a differential emission measure (DEM) distribution. The DEM distribution spans a broad range in ξ (Δ log ξ 2) and is centered around log ξ = 2.5. We find that the total emission measure of the visible portion of the highly ionized wind is ~3 × 1056 cm-3. The qualitative aspects of the inferred DEM distribution are consistent with a wind model derived from the Hatchett & McCray picture of an X-ray source immersed in a stellar wind with a generalized Castor, Abbott, & Klein velocity profile. Using this formalism, theoretical DEM distributions, parameterized only by a mass-loss rate and a wind velocity profile, are calculated and used to predict the detailed X-ray spectrum, which is then compared to the ASCA data. Again, we find a statistically acceptable fit (χ = 1.01), with a best-fit mass-loss rate of ~2.7 × 10-7 M☉ yr-1. This is approximately a factor of 10 lower than previous estimates of the mass-loss rate for the Vela X-1 companion star, which have primarily been determined from C IV and Si IV P Cygni profiles, and X-ray absorption measurements. We argue that this discrepancy can be reconciled if the X-ray-irradiated portion of the wind in Vela X-1 is structurally inhomogeneous, consisting of hundreds of cool, dense clumps embedded in a hotter, more ionized gas. Most of the mass is contained in the clumps, while most of the wind volume (>95%) is occupied by the highly ionized component. We show quantitatively that this interpretation is also consistent with the presence of the X-ray fluorescent lines in the ASCA spectrum, which are produced in the cooler, clumped component.

Deriving albedo maps for HAPEX-Sahel from ASAS data using kernel-driven BRDF models

Abstract. This paper describes the application and testing of a method for deriving spatial estimates of albedo from multi-angle remote sensing data. Linear kernel-driven models of surface bi-directional reflectance have been inverted against high spatial resolution multi-angular, multi- spectral airborne data of the principal cover types within the HAPEX-Sahel study site in Niger, West Africa. The airborne data are obtained from the NASA Airborne Solid-state Imaging Spectrometer (ASAS) instrument, flown in Niger in September and October 1992. The maps of model parameters produced are used to estimate integrated reflectance properties related to spectral albedo. Broadband albedo has been estimated from this by weighting the spectral albedo for each pixel within the map as a function of the appropriate spectral solar irradiance and proportion of direct and diffuse illumination. Partial validation of the results was performed by comparing ASAS reflectance and derived directional-hemispherical reflectance with simulations of a millet canopy made with a complex geometric canopy reflectance model, the Botanical Plant Modelling System (BPMS). Both were found to agree well in magnitude. Broadband albedo values derived from the ASAS data were compared with ground-based (point sample) albedo measurements and found to agree extremely well. These results indicate that the linear kernel-driven modelling approach, which is to be used operationally to produce global 16 day, 1 km albedo maps from forthcoming NASA Earth Observing System spaceborne data, is both sound and practical for the estimation of angle-integrated spectral reflectance quantities related to albedo. Results for broadband albedo are dependent on spectral sampling and on obtaining the correct spectral weigthings.

Iron Line Diagnostics of the Postshock Hot Plasma in MagneticCataclysmic Variables Observed with ASCA

The ASCA spectra of ~20 magnetic cataclysmic variables are presented. Owing to the high spectral resolution of the solid-state imaging spectrometer, we successfully resolved the iron Kα emission line into the fluorescent (6.4 keV) and plasma (6.7 and 7.0 keV) components. By comparing the ionization temperature, which is obtained from the intensity ratio of the plasma line components of iron, with the continuum temperature, we have obtained the evidence that the postshock plasma has a temperature distribution. Detailed analysis indicates that the observed temperature distribution is consistent with that expected from the postshock plasma model in the bremsstrahlung cooling domain. In the framework of this postshock plasma model, we have constrained the mass of the white dwarf in totally nine intermediate polars and obtained the iron abundances. The obtained masses are generally consistent with the previous X-ray work. We have found that the iron abundance is generally subsolar, and its distribution probably peaks at 0.2-0.6 solar. We have also shown that the reflection from the white dwarf surface makes significant contribution to the observed fluorescent iron Kα emission line.

The X‐Ray Iron Emission from Tycho's Supernova Remnant

We present the results of broadband spectral model fits to the X-ray spectrum of Tycho's supernova remnant obtained by the Solid-State Imaging Spectrometers on the ASCA Observatory. We use single temperature, single ionization age, nonequilibrium ionization models to characterize the ejecta and the blast-shocked interstellar medium. Previous spectral studies have suggested that the Fe ejecta in this Type Ia remnant are stratified interior to the other ejecta. These studies, however, have generally restricted their attention to the Fe K blend at 6.5 keV. ASCA provides data over a broad energy range that allow the placement of important constraints simultaneously from the Fe L emission near 1 keV, as well as the Fe K emission. We find that the simplest models, with emission from the ejecta and blast wave each at a single temperature and ionization age, severely underestimate the flux in the Fe K blend. These models also show that there is little Fe emission associated with the Si and S ejecta shell, which has an average temperature kT ~ 0.86 keV and ionization age net ~ 1011 cm-3 s. The blast-shocked interstellar medium has abundances roughly 0.3 times the solar value, while the ejecta—with the exception of Fe—have relative abundances that are typical of Type Ia supernovae. The addition of another component of Fe emission—which we associate with ejecta—at a temperature at least 2 times higher and an ionization age ~100 times lower than the Si ejecta does provide a good fit to the spectrum. This model is consistent with imaging results. Although fluorescent emission from dust in the remnant may contribute to the Fe K flux, we conclude that it is unlikely to be the dominant component.

A Broadband X‐Ray Study of the Young Neutron Star PSR B1706−44

The young Vela-like neutron star PSR B1706-44 was imaged by both the HRI aboard ROSAT and the solid-state imaging spectrometers and gas imaging spectrometers aboard ASCA during a 6 month period in late 1994 and early 1995. The broadband data set, extending over two decades in energy, allowed a detailed spatial, spectral, and temporal study to be conducted. PSR B1706-44 is found embedded in a compact synchrotron nebula of physical size ~0.32 pc and displays the morphology characteristic of the other young neutron stars in the 104-105 yr age range. No pulsations at the radio period were detected in either the ROSAT or the ASCA data. The spectrum is well described by a power-law distribution, and the data are consistent with there being no spectral break from the radio through the soft X-ray band. The unpulsed TeV emission that has been observed from PSR B1706-44 can be reconciled with these observations if the TeV emission results from the up-scattering of background IR photons by the population of high-energy particles that produce the soft X-ray photons.

An ASCA Observation of the X-Ray Binary GX 301-2

view Abstract Citations (29) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An ASCA Observation of the X-Ray Binary GX 301-2 Saraswat, P. ; Yoshida, A. ; Mihara, T. ; Kawai, N. ; Takeshima, T. ; Nagase, F. ; Makishima, K. ; Tashiro, M. ; Leahy, D. A. ; Pravdo, S. ; Day, C. S. R. ; Angelini, L. Abstract The X-ray binary pulsar GX 301-2 was observed with the Advanced Satellite for Cosmology and Astrophysics (ASCA) on 1994 February 13-14, at the binary orbital phase between 0.277 and 0.308. The source was found to be in a low-intensity phase, with an intrinsic luminosity Lx = 6.6 x 1035 ergs s-1 in the 0.7-10.0 keV energy band. This is roughly 2 orders of magnitude lower than the peak luminosity generally observed at periastron. The spectral analysis shows the presence of a strong low-energy excess below about 4 keV and high photoelectric absorption (∼6 x 1023 cm-2). Part of the soft excess may be caused by the scattering of X-rays around a region of increased density by the less dense ambient stellar wind, which would explain the absence of pulsations in the low-energy excess. The spectrum also shows a strong, narrow fluorescent iron line and an absorption iron K edge. The average energy of the line is 6.400±0.008 keV and that of the edge is 7.183±0.013 keV (at the 90% confidence level). The iron line equivalent width is 228±18 eV. The partial covering model does not describe the low-energy excess adequately. It underestimates the continuum between 2.0 and 5.0 keV but overestimates it below 1.5 keV. This, together with the absence of pulsations in the low-energy excess, rules out the partial covering model as a good description of the continuum spectrum. In addition, the spectra from the solid-state imaging spectrometers (SI S) aboard ASCA reveal two new features. First, it is seen that the fit with the scattering model is not acceptable below 2 keV and suggests an additional component as cause for this residual soft excess. The ultrasoft component has been observed in the spectra of GX 301-2 for the first time and can be fitted well by thermal emission from a hot plasma with a temperature kT of ∼0.8 keV. The ultrasoft component may arise because of emission from X-ray-induced shocks in the gas trailing the neutron star. A partial ionization model with a warm absorber in series with a neutral absorber, including scattering, does not account for the ultrasoft excess below 1.5 keV and can be ruled out. Second, it is also seen that the SIS spectrum is dominated by line features at 0.80, 1.73, 2.30, 2.98, and 3.68 keV. These can be identified with the fluorescent line emission from neutral or near-neutral Ne, Si, S, Ar, and Ca, respectively. This implies that the line emission is coming from cold (≤ 105 K) gas. The pulse phase spectroscopy shows that the photon index, the iron line intensity, and the equivalent width vary with pulse phase. The large equivalent width variations are, however, mainly due to the changes in the underlying continuum intensity. Publication: The Astrophysical Journal Pub Date: June 1996 DOI: 10.1086/177285 Bibcode: 1996ApJ...463..726S Keywords: STARS: BINARIES: CLOSE; STARS: PULSARS: INDIVIDUAL ALPHANUMERIC: GX 301-2; X-RAYS: STARS full text sources ADS | data products SIMBAD (3) HEASARC (1)

ASCA solid state imaging spectrometer observations of O stars

We report ASCA Solid State Imaging Spectrometer (SIS) X-ray observations of the O stars delta Ori and lambda Ori. The energy resolution of the SIS allows us to resolve features in the O star X-ray spectra which are not apparent in spectra obtained by X-ray spectrometers with lower energy resolution. SIS spectra from both stars show evidence of line emission, suggesting the thermal nature of the X-ray source. However, the observed line strengths are different for the two stars. The observed stellar X-ray spectra are not well described by isothermal models although absorbed thermal emission models with two or more temperatures can provide an adequate fit to the data. For both stars we present evidence of absorbing columns significantly larger than the known Interstellar Medium (ISM) columns, indicative of absorption by a circumstellar medium, presumably the stellar winds. In addition, the lambda Ori spectrum shows the presence of emission at energies greater than 3 keV which is not seen in the delta Ori spectrum.

ASCA observations of SS Cygni during an anomalous outburst

SS Cygni was observed by the ASCA satellite on 1993 May 27, the first cataclysmic variable studied by ASCA. The observations were conducted while the system was in an outburst of the 'anomalous' variety. The SIS spectrum cannot be explained by two-temperature Raymond-Smith coronal plasma models as invoked in previous studies with lower spectral resolution. Significantly better agreement is found for models with plasma emission at kT = 0.8, 3.5 keV and thermal bremsstrahlung at kT = 18 keV. The gas imaging spectrometer (GIS) data are consistent with the solid state imaging spectrometer (SIS) data, showing evidence for Fe line emission but showing no evidence of pulsation over times ranging from seconds to minutes. These observations seem at variance with standard theory in two regards: we simultaneously see hard X-rays and optically thin soft X-rays while the system is in outburst, and we see a nonsmooth emission measure distribution. We speculate on possible scenarios which might resolve these differences.

ASCA observation of NGC 4636: Dark matter and metallicity gradient

We present our analysis of ASCA PV phase observation of the elliptical galaxy NGC 4636. Solid state imaging spectrometer (SIS) spectra in six concentric annuli centered on NGC 4636 are used to derive temperature, metallicity, and column density profiles for the hot interstellar medium. Outside of the central 3 min the temperature is roughly constant at approximately 0.85 keV, while the metallicity decreases from greater than 0.36 solar at the center to less than 0.12 solar at R approximately 9 min. The implications of this gradient for elliptical galaxy formation and the enrichment of intracluster gas are discussed. We derive a detailed mass profile consistent with the stellar velocity dispersion and with ROSAT position sensitive proportional counter (PSPC) and ASCA SIS X-ray temperature profiles. We find that NGC 4636 becomes dark matter dominated at roughly the de Vaucouleurs radius, and, at r approximately 100 kpc, the ratio of dark to luminous matter density is approximately 80 and solar mass/solar luminosity approximately equal to 150. Evidence for the presence of a cooling flow is also discussed.

ASCA X-ray spectra of the active single stars Beta Ceti and pi(1) Ursae Majoris

view Abstract Citations (60) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS ASCA X-Ray Spectra of the Active Single Stars beta Ceti and pi 1 Ursae Majoris Drake, S. A. ; Singh, K. P. ; White, N. E. ; Simon, Theodore Abstract We present X-ray spectra obtained by ASCA of two single, active stars, the G dwarf pi(1) UMa, and the G9/K0 giant Beta Cet. The spectra of both stars require the presence of at least two plasma components with different temperatures, 0.3-0.4 keV and approximately 0.7 keV, in order for acceptable fits to be obtained. The spectral resolving power and signal-to-noise ratio of the solid state imaging spectrometer (SIS) spectra allow us to formally constrain the coronal abundances of a number of elements. In Beta Cet, we find Mg to be overabundant, while other elements such as O, Ne, and N are underabundant, relative to the solar photospheric values. From the lower signal-to-noise ratio SIS spectrum of pi(1) UMa, we find evidence for underabundances of O, Ne, and Fe. These results are discussed in the context of the present understanding of elemental abundances in solar and stellar coronae. Publication: The Astrophysical Journal Pub Date: November 1994 DOI: 10.1086/187639 Bibcode: 1994ApJ...436L..87D Keywords: Abundance; Binary Stars; Dwarf Stars; Giant Stars; Stellar Composition; X Ray Spectra; Imaging Spectrometers; Signal To Noise Ratios; Stellar Coronas; Astrophysics full text sources ADS | data products SIMBAD (4) HEASARC (1)

ASCA measurements of the grain-scattered X-ray halos of eclipsing massive X-ray binaries: VELA X-1 and Centaurus X-3

view Abstract Citations (34) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS ASCA Measurements of the Grain-scattered X-Ray Halos of Eclipsing Massive X-Ray Binaries: VELA X-1 and Centaurus X-3 Woo, Jonathan W. ; Clark, George W. ; Day, Charles S. R. ; Nagase, Fumiaki ; Takeshima, Toshiaki Abstract We have measured the decaying dust-scattered X-ray halo of Cen X-3 during its binary eclipse with the ASCA solid-state imaging spectrometer (SIS). The surface brightness profile (SBP) of the image in the low-energy band (0.5-3 keV) lies substantially above the point-spread function (PSF) of the X-ray telescope, while the SBP in the high-energy band (5-10 keV) exhibits no significant deviation. By contrast, the SBPs of Vela X-1 during its eclipse are consistent with the PSF in both the low- and high-energy bands -- strong evidence that a dust halo is indeed present in Cen X-3. Accordingly, we modeled the SBP of Cen X-3 taken from six consecutive time segments under the principal assumptions that the dust is distributed uniformly along a segment of the line of sight, the grains have a power-law size distribution, and the low-energy source flux was the same function of orbital phase before as during our observation. The best-fit set of parameters included a grain density value of 1.3 g/cu cm, substanially less than the density of 'astronomical silicate.' This result supports the idea that interstellar grains are 'fluffy' aggregates of smaller solid particles. We attribute the failure to detect a halo of Vela X-1 during its eclipse phase to extended strong circumsource absorption that probably occurred before the eclipse and allowed the halo to decay away before the observation began. Publication: The Astrophysical Journal Pub Date: November 1994 DOI: 10.1086/187620 Bibcode: 1994ApJ...436L...5W Keywords: Eclipsing Binary Stars; Halos; Massive Stars; Pulsars; X Ray Binaries; X Ray Scattering; Imaging Spectrometers; Interstellar Matter; Light Curve; Astrophysics; STARS: BINARIES: ECLIPSING; ISM: DUST; EXTINCTION; STARS: PULSARS: INDIVIDUAL NAME: VELA X-1; STARS: PULSARS: INDIVIDUAL NAME: CENTAURUS X-3; X-RAYS: STARS full text sources ADS | data products SIMBAD (3) HEASARC (1)